1. Field of the Invention
The present invention relates to an embedded magnetic component transformer device, and in particular to an embedded magnetic component transformer device with reduced coupling and improved isolation properties.
2. Description of the Related Art
It is known, for example, in US 2011/0108317 A1, to provide low profile transformers and inductors in which the magnetic components are embedded in a cavity in a resin substrate, and the necessary input and output electrical connections for the transformer or inductor are formed on the substrate surface. A printed circuit board (PCB) for a power supply device can then be formed by adding layers of solder resist and copper plating to the top and/or bottom surfaces of the substrate. The necessary electronic components for the device may then be surface mounted on the PCB.
Compared to conventional transformers, an embedded design allows a significantly thinner and more compact device to be built. This is desirable because typically the space available for mounting the transformer device onto a PCB, for example, a motherboard of an electronics device, will be very limited. A transformer component with a smaller footprint will therefore enable more components to be mounted onto the PCB, or enable the overall size of the PCB and therefore the entire device to be reduced.
When reducing the size of the transformer device, the gap between adjacent turns on a transformer winding are likely to be provided more closely together, and the gap between separate windings provided on the transformer will also be reduced. This reduces the ease with which a magnetic field, set up in the transformer during use, can escape from the transformer core and therefore results in a stronger coupling, via the magnetic field, between the separate windings provided on the core. Another consequence of reducing the gap between adjacent turns is an increase in the capacitance existing between adjacent conducting components which include the transformer windings. Such increased coupling between the windings via the magnetic field they generate, and such increased distributed capacitance throughout the transformer, are not desirable properties for a transformer in certain applications.
Furthermore, reducing the transformer size can result in safety considerations, particularly if two separate windings sharing a common transformer core are to handle high voltages. Such a transformer is used in power electronics applications and power converter technology, for example. In this case, the windings must be electrically isolated from one another. A smaller transformer will tend to reduce the distance between electrically isolated windings, meaning that the electrical isolation is less robust against failure by electrical arcing and reducing the maximum voltages that the transformer windings can safely handle.
The electrical isolation can be increased to a safe level by using a multi-layer PCB arrangement with different windings provided on different PCB layers, by providing a cover on the transformer core, or by coating the windings in a conformal coating or other sort of insulating material such as insulating tape. Triple insulated wire can also be used. However, all of these techniques have the disadvantage that the embedded magnetic component transformer device must be made larger to accommodate the extra PCB layers or the thicker insulation on the windings and/or core.
It would be desirable to provide an embedded transformer device having reduced coupling between the coils and improved isolation characteristics, and to provide a method for manufacturing such a device.